rear wheel bearing

[dberman]

I have a '85 Carrera that is mostly a track car. I am getting the car ready for the season and was checking the rear wheel bearings. When I pulled on the left rear wheel there was alot of play in it so I figured the wheel bearing needed replacement. However I noticed that the castellated nut on the end of the shaft seemed a little loose. It had a cotter pin through it that wasn't damaged so I figured the nut couldn't have loosened up but when I remove the pin and torqued down the nut, it turned 1/8th of a turn. Now the wheel seems tight and everything seems good. The wheel turns smoothly.

I can't figure out how the nut loosened up. I must be missing something. Any ideas?

Thanks.

[rusnak]

There is a LOT of torque required on that nut. Something north of 240 ft/ lbs IIRC. You have to use a 3/4" wrench and stand on it. Very possible that it wasn't torqued correctly to start with.

[dberman]

Rusnak, I've been tracking the car for the past 3 years and haven't touched those nuts. The wheels have been checked for play before every track event. So those nuts couldn't have been loose all along. Again, there is a cotter pin inserted through the shaft and the nut so I don't think it could have loosened up either.

[jason2guy]

i would go back and really tighten that thing. the advice on the 3/4 breaker bar is good.

[DRACO A5OG]

Go to Harbor Freight and get yourself a 3/4" Torque Wrench and 1/2" socket adaptor. Both are very cheap and you don't have to guess.

[dberman]

I have a torque wrench that is big enough to handle the job (217-230 fl-lbs). My question isn't how to torque the nut properly. The question is how it could have loosened up if there is a cotter pin through the nut. It couldn't have turned with the cotter pin inserted.

[mreid]

There's a good chance that either the previous owner tightened it like you would the front bearing or your track day stress pulled the stub axle tighter into the hub. It only needs about 1mm for the nut the feel loose. On a track car, all suspension components should be checked before each session. You'll be surprised what loosens up or falls off!

[DRACO A5OG]

+1 PO did not torque it properly.

You are lucky, normally, you can not tell the rears are loose. You would hear a "clunk". I would also check the other side is torqued properly. Especially being a track guy.

[Walt Fricke]

I think your bearing is probably going. Another possibility is that the shaft has cracked, elongating it (in which case replacement right now is in order). You should be able to discern, at least on a car with a muffler, a difference in noise between a hard left or a hard right.

Pulling the shaft to check it for cracks is a bit of a pain, but not as much work as pulling the bearing and replacing it. I have a spare shaft (the part the CV bolts to) in my trailer, along with nut and washer, because I've seen these break at the track. The caliper and rotor keep the wheel from flying off, but the nut and washer are lost out there on the track.

But these bearings are heavily loaded, and don't last forever. I've replaced about three (various sides) in 25 years on my SC. Maybe four, having guessed wrong as to which one was bad. When you get them out, you see the pitting in the races, or the balls, or both.

The output flange can crack also (symptom is having to pump brakes, because play has pushed pistons way back), so I have one of those in the spares box.

[Trackrash]

You need to check the torque spec. On the older cars it was 210 -250 IIRC. On the Carreras it is over 300lbs ft.

If you have checked for play with the car jacked up and found none previously, as Walt said, I would be concerned about an impending failure.

BTW, when torquing the nut DO NOT use GREASE on the threads, only oil. Ask me how I know.

[dberman]

The early carreras 84 and some 85's have a different axle configuration. The torque for these are 217-231 ft-lb. The later carreras are 339 ft-lb.

Thanks for your comments Walt. What you are saying makes sense.

[CCM911]

Mine went loose after a while, and the nut had not moved. Just try torquing the bolt and see what happens.

[GH85Carrera]

When I replaced my rear wheel bearings on my 85 I did my best guess torque. Using a 3 foot wrench pushing down 113 lbs. I stood on the bathroom scale and pushed down unit I weighed 113 lbs less than normal on the scale while holding the spot 36 inches from the nut.

Then I stopped at a friends workplace that works on tractor trailers. A mechanic pulled out a huge torque wrench and I handed him my socket and he torqued both nuts to the proper settings. I had guessed pretty close, but now I had science to let me know I was correct. I gave the mechanic 20 bucks and left.

[zippy_gg]

Is it possible that the bearing was not all the way in and that with time and the G forces from tracking the car the bearing worked its way in, now leaving a small gap?
This would also mean that whomever installed the bearing probably didn't torque properly to begin with.

[McLaren-TAG]

Probably worth while to disassemble and inspect, just for the hell of it. Better safe than sorry. In the end you either had loose nut which was clearly causing play and now you've tightened it and it's all good.

Or you have something else more, more serious that warrants inspection. I wouldn't just let it go.

[Trackrash]

Not to hyjack, but I wonder, is there a spec or wear limit for rear bearings?

I have never been able to get my driver's side to be "tight". I'm on my third bearing and there is always a small amount of play.

Here I am measuring about .003" of play after the bearing was re-torqued. It seemed tight at first, but after a few thousand miles there was noticeable play.


It's an SKF, if that makes any difference.

[DRACO A5OG]

^^^ sorry to say, your hub may be compromised but I am sure you have guessed that already. .003? how much run out if any on the passenger side?

[Trackrash]

On the passenger side there is no play. However there seems to be a bit of "flex" if you apply pressure back and forth at the top of the wheel.

The last time I replaced the bearing I de-burred the shaft where it contacts the bearing.

No sure what you mean by compromised, should I do a crack test on the axle?

FWIW, the play has not been increasing since I last re-torqued the nut.

It just seems like the bearing has worn in and there is just a small amount of play.
That's why I was wondering if there is a wear limit or if the SKF bearings are prone to this sort of issue?

[rusnak]

Just my $.02. I'd try a new bearing if it were my car.

[wayner]

mine was a little lose too...


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